Multispectral Interferometric Scattering MicroscopyImaging of Gold and Silver Nanoparticles

Noble metal nanoparticles (NPs) exhibit localized plasmon resonances whose peak wavelengths are determined by their size, shape, and composition, providing multicolor labels for optical sensing and imaging. In this work, three-color interferometric scattering microscopy (iSCAT) was applied to image gold (Au) and silver (Ag) NPs with diameters between 5 and 60 nm on three separate wavelength channels: 405, 445, and 520 nm. The three-color detection provides information about the wavelength-dependence of the iSCAT contrast of the individual NP scatterers, which depends on the spectral position of their plasmon resonance. The resulting multispectral iSCAT contrast yields some selectivity and aids the distinction between NPs of the same metal with different sizes as well as between NPs of the same size but different metals. The gain in spectral information paves the path toward multiplexed iSCAT imaging and sensing using NP metal labels of different colors.